Corresponding author
Arianna Pani
Assistant Professor of Pharmacology
Assistant Director of the Postgraduate School of Clinical Pharmacology and Toxicology
Department of Oncology and Hemato-Oncology
University of Milan
Mailing address:
Department of Oncology and Onco – Hematology, Italy
e-mail- arianna.pani@unimi.it
Phone: ++39-0250316950
Fax: ++39-0250317050
ABSTRACTBackground - Since SARS-CoV-2 spread, evidence regarding sex differences in progression and prognosis of COVID-19 have emerged. Besides this, studies on patients’ clinical characteristics have described electrolyte imbalances as one of the recurrent features of COVID-19.Methods - We performed a case-control study on all patients admitted to the emergency department (ED) from 1st March to 31st May 2020 who had undergone a blood gas analysis and a nasopharyngeal swab test for SARS-CoV-2 by rtPCR. We defined positive patients as cases and negatives as controls. The study was approved by the local ethics committee Area 3 Milan. Data were automatically extracted from the hospital laboratory SQL-based repository in anonymized form. We considered as outcomes potassium (K+), sodium (Na+), chlorine (Cl-) and calcium (Ca++) as continuous and as categorical variables, in their relation with age, sex and SARS-CoV-2 infection status.Results - We observed a higher prevalence of hypokalemia among patients positive for SARS-CoV-2 (13.7% vs 6% of negative subjects). Positive patients had a higher probability to be admitted to the ED with hypokalemia (OR 2.75, 95% CI 1.8-4.1 p<0.0001) and women were twice as likely to be affected than men (OR 2.43, 95% CI 1.67-3.54 p<0.001). Odds ratios for positive patients to manifest with an alteration in serum Na+ was (OR 1.6, 95% CI 1.17-2.35 p<0.001) and serum chlorine (OR 1.6, 95% CI 1.03-2.69 p<0.001). Notably, OR for positive patients to be hypocalcemic was 7.2 (95% IC 4.8-10.6 p<0.0001) with a low probability for women to be hypocalcemic (OR 0.63, 95% IC 0.4-0.8 p=0.005).Conclusions - SARS-CoV-2 infection is associated with a higher prevalence of hypokalemia, hypocal- cemia, hypochloremia and sodium alterations. Hypokalemia is more frequent among women and hypocal- cemia among men.What is already known about this topic?Since SARS-CoV-2 spread, evidence regarding sex differences in progression and prognosis of COVID-19 have emerged. Besides, studies on patients’ clinical characteristics have described electrolyte imbalances as one of the recurrent features of COVID-19.What does this article add?We observed a higher prevalence of hypokalemia in patients positive for SARS-CoV-2, and women were twice as likely to be affected than men. Positive patients also had a higher prevalence of hypocalcemia, hypochloremia and sodium alteration. Hypokalemia appears to be more frequent among women and hypocalcemia among men. INTRODUCTION Since December 2019 the world has been struggling to fight the novel coronavirus SARS-CoV-2. As soon as the virus spread in China, researchers noticed the higher predisposition of men to contract COVID-19 [1, 2]. Evidences emerged subsequently revealed also an association between male sex and a more severe disease and death [3, 4]. Some authors have attributed the reasons for these differences to sex differences in immune response [5], to differences in the prevalence of smoking subjects among men and women [6] and to genetics [7]. Few studies have investigated the impact of sex differences in clinical manifestations of the disease other than disease severity and mortality. Early studies on COVID-19 have highlighted the association between the disease and sodium (Na+), potassium (K+), calcium (Ca++) and chloride (Cl-) abnormalities [1, 8, 9]. Chen et al. [10] described a high prevalence of hypokalemic subjects among patients hospitalized with COVID-19. Furthermore, the severity of the disease was associated with a higher degree of hypokalemia. Authors have also shown, in a small sample of patients, that hypokalemic subjects had a higher mean urinary K+ output than non-hypokalemic patients, suggesting a possible implication for increased K+ urine loss. This mechanism could be explained by the disruption caused by the binding of SARS-CoV-2 to angiotensin-converting enzyme 2 (ACE2) with a possible impact on the renin-angiotensin system (RAS). Despite the aforementioned evidences, little is still known regarding electrolyte disturbances in COVID-19 and in SARS-CoV-2 infection. The aim of this study was to examine the prevalence of electrolyte imbalances among patients with SARS- CoV-2 infection in a large cohort and its distribution according to age and sex. Sex differences in electrolyte imbalances caused by SARS-CoV2: a case-control study METHODS The study protocol was approved by the Ethics Committee Area 3 Milano (prot. 92–15032020). Signed informed content was obtained for each participant. This study was conducted in accordance with the principles of the 1964 Declaration of Helsinki. Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guidelines.DATA SOURCESThis case-control study has been performed at the ASST GOM Niguarda Hospital in Italy. At our hospital, we store all analytical results of the tests performed in the laboratory in an SQL-based repository. With the purpose to conduct this study, a query was created to extract data with no personal information other than gender and date of birth. This query extracted laboratory results based on the date of execution, the requesting department and the type of service performed. The fields extracted were: patient’s ID (a numeric string that uniquely identifies the patient without personal data), sex, birth date day of lab tests execution (with a truncation for the extracted data referred to the period 1st March - 31st May), tests ID, tests results, hospital ward. In this way we were able to collect the biochemical and microbiological profile of patients at admittance to the emergency department (ED) and categorize patients based on their positivity (or negativity) to SARS-CoV-2, sex and age.STUDY PATIENTS AND COVARIATESWe considered a cohort of patients admitted to the ED from 1st March to 31st May 2020 and screened for SARS-CoV-2 infection. Inclusion criteria were: age over 18 years and the performance, during the per- manence in the Emergency Department, of at least one blood gas analysis (both arterial and venous) performed using POC Siemens RAPIDPoint 500 Blood Gas System. Compared to central Laboratory analyzers, results obtained from POC Siemens RAPIDPoint 500 blood gas system are stackable for all tested parameters taken into consideration in this study. These results are warranted for our own procedures and devices [11]. We collected data regarding electrolyte profile, pH, blood glucose, white blood cell counts, lymphocyte counts, neutrophils, creatinine. We defined cases and controls according to the positivity or negativity to the nasopharyngeal swab test for SARS-CoV-2 by rtPCR (GeneFinder TMCOVID-19 Plus RealAmp Kit, ELITech; Allplex TM2019- nCoV Assay, Seegene) performed according to the World Health Organization (WHO) guidance. Positive patients were defined as cases and negatives as controls. Patients were then categorized in three classes according to age (under 65 years, between 65 and 75 years and over 75 years) and according to sex and age range combined into six groups: i) Females aged below 65 years; ii) Females aged between 65 and 75 years; iii) Females aged over 75 years; iv) Males aged below 65 years; v) Males aged between 65 and 75 years; vi) Males aged over 75 years.OUTCOMESAs outcomes, we considered potassium (K+), sodium (Na+), chloride (Cl-) and calcium (Ca++) both as continuous and as categorical variables, in their relationship with age, sex and SARS-CoV-2 infection status. We defined imbalances of K+, Na+, Cl- and Ca++, according to ranges presented in Table 1. Leveraging the fact that a blood gas analysis was performed on the majority of patients accepted to the ED, we decided to consider the electrolyte values deriving from this analysis, to avoid potential bias due to the comparison of different methods. We analyzed potential effect modifiers such as renal disease, by calculating eGFR using the MDRD formula [12]. To get closer to precision medicine, it would be preferable to have all the information available in electronic form and the Human Phenotype Ontologies (HPO) is a useful tool for this purpose, making information available at different levels of granularity. The power of HPO has been demonstrated to enrich clinical data, including infectious diseases [13] and for this, to describe outcomes we use the terms of the ”Human Phenotype Ontology” (HPO) to better promote the link between SARS-CoV2 to their phenotypes in support of infectious disease research. [Table 1 about here.]STATISTICAL ANALYSISPatients characteristics were summarized with mean and standard deviation for continuous variables and with number and percentages for categorical. Differences between the two cohorts have been tested with t-test and chi-square test, or Fisher exact test, respectively. Assumption of normality distribution was evaluated by Shapiro-Wilk test. A three-way ANOVA test was performed to evaluate differences among sex, class of age and presence of SARS-CoV-2 infection on potassium values. Tukey’s multiple comparisons test was performed for post-hoc comparison. Several logistic regression analyses were performed to evaluate the relationship between SARS-CoV-2 infection and electrolyte imbalances separately. Odds ratios (ORs) and confidence intervals 95% (CI 95%) were reported. Multivariable logistic regression considering SARS-CoV-2 positivity, age group and sex on hypokalemia, hypochloremia, hypocalcemia and abnormal natremia were performed. Odds ratios and CI 95% were reported. P values <0.05 were considered statistically significant. Sex differences in electrolyte imbalances caused by SARS-CoV2: a case-control study RESULTS For the retrospective cohort study of consecutive patients admitted to the ED from 1st March 1 to 31st May 2020 who had undergone blood gas analysis, 1347 patients were included. 710 (53%) patients resulted positive to the nasopharyngeal swabs rtPCR test for SARS-CoV-2 and 619 resulted negative. Patients baseline characteristics between the two groups are summarized in table 2. The case cohort was characterized by a lower prevalence of female subjects (39%, 274/710), lower mean pH and lactate values (7.23 ± 0.37 and 1.72 ± 1.45 mEq/l) and an electrolyte panel significantly different from controls for K+ and Ca (3.80 ± 0.49 vs 4.11 ± 0.62 mEq/l and 1.20 ± 0.10 vs 1.12 ± 0.07 mEq/l respectively). Both cohorts were homogeneous for age, eGFR and renal disease prevalence. The prevalence of patients aged between 65 and 75 years was significantly higher in the SARS-CoV-2 positive cohort (20.6%, 145), while there was a lower prevalence of patients aged under 75 years (30.2%, 212). [Table 2 about here.]POTASSIUMWe analyzed the distribution of serum K+ values as a continuous parameter with a three-way ANOVA on the basis of SARS-CoV-2 positivity or negativity, three classes of ages (years >65; 65 to 75; >75) and sex. Results showed a clusterization (Figure 1) of serum K+ values according to those parameters, and in particular to SARS-CoV-2 status. We then divided cases and controls cohorts according to their kalemic state (Table 3) and observed a higher prevalence of patients with hypokalemia in the group with SARS-CoV-2 infection. [Table 3 about here.] Further analyses of the population according to sex and class of age (Table 4) allowed us to observe a higher prevalence of hypokalemic patients among woman positive for SARS-CoV2. The prevalence was similar for all classes of age. The difference between positive and negative patients was statistically significant for men below 65 years (p=0.013), women below 65 years (p<0.001). In women over 75 years it was possible to note a difference which did not reach statistical significance (p=0.069).